8 Entropy is a measure of the disorder of a system.

1. (a)Assume the entropy, S, for H2O is zero at 0 K. Sketch a graph on the axes to show how the entropy changes for H2O between 0 K and 300 K. [Figure: Graph axes with S/JK⁻¹mol⁻¹ on y-axis and temperature/K on x-axis from 0 to 300 K.] [2][2]
2. (b)Place one tick (✔) in each row of the table to show the sign of the entropy changes, ΔS. | ΔS is negative | ΔS is positive ---|---|--- solid dissolving in water | | water boiling to steam | | [1][1]
3. (c)The equation for a reaction that produces methanol is shown. CO2(g) + 3H2(g) → CH3OH(g) + H2O(g) Use relevant bond energies from the Data Booklet to calculate the enthalpy change, ΔH, for this gas phase reaction. ΔH = ................................. kJ mol⁻¹ [2][2]
4. (d)At 298 K, both products of this reaction are liquid. CO2(g) + 3H2(g) → CH3OH(l) + H2O(l) Standard entropies are shown in the table. substance | CO2(g) | H2(g) | CH3OH(l) | H2O(l) ---|---|---|---|--- S°/JK⁻¹mol⁻¹ | +214 | +131 | +127 | +70
5. (d)(i)Calculate the standard entropy change, ΔS°, for this reaction. ΔS° = ................................. JK⁻¹mol⁻¹ [2][2]
6. (d)(ii)Calculate the standard Gibbs free energy change, ΔG°, for this reaction at 298 K. ΔG° = ................................. kJ mol⁻¹ [2][2]
7. (d)(iii)Predict the effect of increasing the temperature on the feasibility of this reaction. [1][1]
8. (e)In a methanol-oxygen fuel cell, CH3OH(l) and O2(g) are in contact with two inert electrodes immersed in an acidic solution. The half-equation for the reaction at the methanol electrode is shown. CH3OH + H2O ⇌ CO2 + 6H+ + 6e⁻ E° = -0.02 V
9. (e)(i)Use the Data Booklet to write an equation for the overall cell reaction. [1][1]
10. (e)(ii)Use E° values to calculate the E°cell for this reaction. E°cell = ................................. V [1][1]

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